/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.yimixian.app.common;

import javax.annotation.Nullable;

/**
 * Static convenience methods that help a method or constructor check whether it
 * was invoked correctly (whether its <i>preconditions</i> have been met). These
 * methods generally accept a {@code boolean} expression which is expected to be
 * {@code true} (or in the case of {@code checkNotNull}, an object reference
 * which is expected to be non-null). When {@code false} (or {@code null}) is
 * passed instead, the {@code Preconditions} method throws an unchecked
 * exception, which helps the calling method communicate to <i>its</i> caller
 * that <i>that</i> caller has made a mistake. Example:
 * 
 * <pre>
 * {@code
 * 
 *   /**
 *    * Returns the positive square root of the given value.
 *    *
 *    * @throws IllegalArgumentException if the value is negative
 *    *}{@code /
 *   public static double sqrt(double value) {
 *     Preconditions.checkArgument(value >= 0.0, "negative value: %s", value);
 *     // calculate the square root
 *   }
 * 
 *   void exampleBadCaller() {
 *     double d = sqrt(-1.0);
 *   }}
 * </pre>
 *
 * In this example, {@code checkArgument} throws an
 * {@code IllegalArgumentException} to indicate that {@code exampleBadCaller}
 * made an error in <i>its</i> call to {@code sqrt}. <h3>Warning about
 * performance</h3>
 * <p>
 * The goal of this class is to improve readability of code, but in some
 * circumstances this may come at a significant performance cost. Remember that
 * parameter values for message construction must all be computed eagerly, and
 * autoboxing and varargs array creation may happen as well, even when the
 * precondition check then succeeds (as it should almost always do in
 * production). In some circumstances these wasted CPU cycles and allocations
 * can add up to a real problem. Performance-sensitive precondition checks can
 * always be converted to the customary form:
 * 
 * <pre>
 * {@code
 * 
 *   if (value < 0.0) {
 *     throw new IllegalArgumentException("negative value: " + value);
 *   }}
 * </pre>
 *
 * <h3>Other types of preconditions</h3>
 * <p>
 * Not every type of precondition failure is supported by these methods.
 * Continue to throw standard JDK exceptions such as
 * {@link java.util.NoSuchElementException} or
 * {@link UnsupportedOperationException} in the situations they are intended
 * for.
 * <h3>Non-preconditions</h3>
 * <p>
 * It is of course possible to use the methods of this class to check for
 * invalid conditions which are <i>not the caller's fault</i>. Doing so is
 * <b>not recommended</b> because it is misleading to future readers of the code
 * and of stack traces. See <a href=
 * "http://code.google.com/p/guava-libraries/wiki/ConditionalFailuresExplained"
 * >Conditional failures explained</a> in the Guava User Guide for more advice.
 * <h3>{@code java.util.Objects.requireNonNull()}</h3>
 * <p>
 * Projects which use {@code com.google.common} should generally avoid the use
 * of {@link java.util.Objects#requireNonNull(Object)}. Instead, use whichever
 * of {@link #checkNotNull(Object)} or {@link Verify#verifyNotNull(Object)} is
 * appropriate to the situation. (The same goes for the message-accepting
 * overloads.)
 * <h3>Only {@code %s} is supported</h3>
 * <p>
 * In {@code Preconditions} error message template strings, only the
 * {@code "%s"} specifier is supported, not the full range of
 * {@link java.util.Formatter} specifiers.
 * <h3>More information</h3>
 * <p>
 * See the Guava User Guide on <a
 * href="http://code.google.com/p/guava-libraries/wiki/PreconditionsExplained"
 * >using {@code Preconditions}</a>.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
public final class Preconditions {
    private Preconditions() {
    }

    /**
     * Ensures the truth of an expression involving one or more parameters to
     * the calling method.
     *
     * @param expression a boolean expression
     * @throws IllegalArgumentException if {@code expression} is false
     */
    public static void checkArgument(boolean expression) {
        if (!expression) {
            throw new IllegalArgumentException();
        }
    }

    /**
     * Ensures the truth of an expression involving one or more parameters to
     * the calling method.
     *
     * @param expression a boolean expression
     * @param errorMessage the exception message to use if the check fails; will
     *            be converted to a string using {@link String#valueOf(Object)}
     * @throws IllegalArgumentException if {@code expression} is false
     */
    public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
        if (!expression) {
            throw new IllegalArgumentException(String.valueOf(errorMessage));
        }
    }

    /**
     * Ensures the truth of an expression involving one or more parameters to
     * the calling method.
     *
     * @param expression a boolean expression
     * @param errorMessageTemplate a template for the exception message should
     *            the check fail. The message is formed by replacing each
     *            {@code %s} placeholder in the template with an argument. These
     *            are matched by position - the first {@code %s} gets
     *            {@code errorMessageArgs[0]}, etc. Unmatched arguments will be
     *            appended to the formatted message in square braces. Unmatched
     *            placeholders will be left as-is.
     * @param errorMessageArgs the arguments to be substituted into the message
     *            template. Arguments are converted to strings using
     *            {@link String#valueOf(Object)}.
     * @throws IllegalArgumentException if {@code expression} is false
     * @throws NullPointerException if the check fails and either
     *             {@code errorMessageTemplate} or {@code errorMessageArgs} is
     *             null (don't let this happen)
     */
    public static void checkArgument(boolean expression,
            @Nullable String errorMessageTemplate,
            @Nullable Object... errorMessageArgs) {
        if (!expression) {
            throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs));
        }
    }

    /**
     * Ensures the truth of an expression involving the state of the calling
     * instance, but not involving any parameters to the calling method.
     *
     * @param expression a boolean expression
     * @throws IllegalStateException if {@code expression} is false
     */
    public static void checkState(boolean expression) {
        if (!expression) {
            throw new IllegalStateException();
        }
    }

    /**
     * Ensures the truth of an expression involving the state of the calling
     * instance, but not involving any parameters to the calling method.
     *
     * @param expression a boolean expression
     * @param errorMessage the exception message to use if the check fails; will
     *            be converted to a string using {@link String#valueOf(Object)}
     * @throws IllegalStateException if {@code expression} is false
     */
    public static void checkState(boolean expression, @Nullable Object errorMessage) {
        if (!expression) {
            throw new IllegalStateException(String.valueOf(errorMessage));
        }
    }

    /**
     * Ensures the truth of an expression involving the state of the calling
     * instance, but not involving any parameters to the calling method.
     *
     * @param expression a boolean expression
     * @param errorMessageTemplate a template for the exception message should
     *            the check fail. The message is formed by replacing each
     *            {@code %s} placeholder in the template with an argument. These
     *            are matched by position - the first {@code %s} gets
     *            {@code errorMessageArgs[0]}, etc. Unmatched arguments will be
     *            appended to the formatted message in square braces. Unmatched
     *            placeholders will be left as-is.
     * @param errorMessageArgs the arguments to be substituted into the message
     *            template. Arguments are converted to strings using
     *            {@link String#valueOf(Object)}.
     * @throws IllegalStateException if {@code expression} is false
     * @throws NullPointerException if the check fails and either
     *             {@code errorMessageTemplate} or {@code errorMessageArgs} is
     *             null (don't let this happen)
     */
    public static void checkState(boolean expression,
            @Nullable String errorMessageTemplate,
            @Nullable Object... errorMessageArgs) {
        if (!expression) {
            throw new IllegalStateException(format(errorMessageTemplate, errorMessageArgs));
        }
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling
     * method is not null.
     *
     * @param reference an object reference
     * @return the non-null reference that was validated
     * @throws NullPointerException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference) {
        if (reference == null) {
            throw new NullPointerException();
        }
        return reference;
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling
     * method is not null.
     *
     * @param reference an object reference
     * @param errorMessage the exception message to use if the check fails; will
     *            be converted to a string using {@link String#valueOf(Object)}
     * @return the non-null reference that was validated
     * @throws NullPointerException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
        if (reference == null) {
            throw new NullPointerException(String.valueOf(errorMessage));
        }
        return reference;
    }

    /**
     * Ensures that an object reference passed as a parameter to the calling
     * method is not null.
     *
     * @param reference an object reference
     * @param errorMessageTemplate a template for the exception message should
     *            the check fail. The message is formed by replacing each
     *            {@code %s} placeholder in the template with an argument. These
     *            are matched by position - the first {@code %s} gets
     *            {@code errorMessageArgs[0]}, etc. Unmatched arguments will be
     *            appended to the formatted message in square braces. Unmatched
     *            placeholders will be left as-is.
     * @param errorMessageArgs the arguments to be substituted into the message
     *            template. Arguments are converted to strings using
     *            {@link String#valueOf(Object)}.
     * @return the non-null reference that was validated
     * @throws NullPointerException if {@code reference} is null
     */
    public static <T> T checkNotNull(T reference,
            @Nullable String errorMessageTemplate,
            @Nullable Object... errorMessageArgs) {
        if (reference == null) {
            // If either of these parameters is null, the right thing happens
            // anyway
            throw new NullPointerException(format(errorMessageTemplate, errorMessageArgs));
        }
        return reference;
    }

    /*
     * All recent hotspots (as of 2009) *really* like to have the natural code
     * if (guardExpression) { throw new BadException(messageExpression); }
     * refactored so that messageExpression is moved to a separate
     * String-returning method. if (guardExpression) { throw new
     * BadException(badMsg(...)); } The alternative natural refactorings into
     * void or Exception-returning methods are much slower. This is a big deal -
     * we're talking factors of 2-8 in microbenchmarks, not just 10-20%. (This
     * is a hotspot optimizer bug, which should be fixed, but that's a separate,
     * big project). The coding pattern above is heavily used in java.util, e.g.
     * in ArrayList. There is a RangeCheckMicroBenchmark in the JDK that was
     * used to test this. But the methods in this class want to throw different
     * exceptions, depending on the args, so it appears that this pattern is not
     * directly applicable. But we can use the ridiculous, devious trick of
     * throwing an exception in the middle of the construction of another
     * exception. Hotspot is fine with that.
     */

    /**
     * Ensures that {@code index} specifies a valid <i>element</i> in an array,
     * list or string of size {@code size}. An element index may range from
     * zero, inclusive, to {@code size}, exclusive.
     *
     * @param index a user-supplied index identifying an element of an array,
     *            list or string
     * @param size the size of that array, list or string
     * @return the value of {@code index}
     * @throws IndexOutOfBoundsException if {@code index} is negative or is not
     *             less than {@code size}
     * @throws IllegalArgumentException if {@code size} is negative
     */
    public static int checkElementIndex(int index, int size) {
        return checkElementIndex(index, size, "index");
    }

    /**
     * Ensures that {@code index} specifies a valid <i>element</i> in an array,
     * list or string of size {@code size}. An element index may range from
     * zero, inclusive, to {@code size}, exclusive.
     *
     * @param index a user-supplied index identifying an element of an array,
     *            list or string
     * @param size the size of that array, list or string
     * @param desc the text to use to describe this index in an error message
     * @return the value of {@code index}
     * @throws IndexOutOfBoundsException if {@code index} is negative or is not
     *             less than {@code size}
     * @throws IllegalArgumentException if {@code size} is negative
     */
    public static int checkElementIndex(
            int index, int size, @Nullable String desc) {
        // Carefully optimized for execution by hotspot (explanatory comment
        // above)
        if (index < 0 || index >= size) {
            throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
        }
        return index;
    }

    private static String badElementIndex(int index, int size, String desc) {
        if (index < 0) {
            return format("%s (%s) must not be negative", desc, index);
        } else if (size < 0) {
            throw new IllegalArgumentException("negative size: " + size);
        } else { // index >= size
            return format("%s (%s) must be less than size (%s)", desc, index, size);
        }
    }

    /**
     * Ensures that {@code index} specifies a valid <i>position</i> in an array,
     * list or string of size {@code size}. A position index may range from zero
     * to {@code size}, inclusive.
     *
     * @param index a user-supplied index identifying a position in an array,
     *            list or string
     * @param size the size of that array, list or string
     * @return the value of {@code index}
     * @throws IndexOutOfBoundsException if {@code index} is negative or is
     *             greater than {@code size}
     * @throws IllegalArgumentException if {@code size} is negative
     */
    public static int checkPositionIndex(int index, int size) {
        return checkPositionIndex(index, size, "index");
    }

    /**
     * Ensures that {@code index} specifies a valid <i>position</i> in an array,
     * list or string of size {@code size}. A position index may range from zero
     * to {@code size}, inclusive.
     *
     * @param index a user-supplied index identifying a position in an array,
     *            list or string
     * @param size the size of that array, list or string
     * @param desc the text to use to describe this index in an error message
     * @return the value of {@code index}
     * @throws IndexOutOfBoundsException if {@code index} is negative or is
     *             greater than {@code size}
     * @throws IllegalArgumentException if {@code size} is negative
     */
    public static int checkPositionIndex(int index, int size, @Nullable String desc) {
        // Carefully optimized for execution by hotspot (explanatory comment
        // above)
        if (index < 0 || index > size) {
            throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
        }
        return index;
    }

    private static String badPositionIndex(int index, int size, String desc) {
        if (index < 0) {
            return format("%s (%s) must not be negative", desc, index);
        } else if (size < 0) {
            throw new IllegalArgumentException("negative size: " + size);
        } else { // index > size
            return format("%s (%s) must not be greater than size (%s)", desc, index, size);
        }
    }

    /**
     * Ensures that {@code start} and {@code end} specify a valid
     * <i>positions</i> in an array, list or string of size {@code size}, and
     * are in order. A position index may range from zero to {@code size},
     * inclusive.
     *
     * @param start a user-supplied index identifying a starting position in an
     *            array, list or string
     * @param end a user-supplied index identifying a ending position in an
     *            array, list or string
     * @param size the size of that array, list or string
     * @throws IndexOutOfBoundsException if either index is negative or is
     *             greater than {@code size}, or if {@code end} is less than
     *             {@code start}
     * @throws IllegalArgumentException if {@code size} is negative
     */
    public static void checkPositionIndexes(int start, int end, int size) {
        // Carefully optimized for execution by hotspot (explanatory comment
        // above)
        if (start < 0 || end < start || end > size) {
            throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
        }
    }

    private static String badPositionIndexes(int start, int end, int size) {
        if (start < 0 || start > size) {
            return badPositionIndex(start, size, "start index");
        }
        if (end < 0 || end > size) {
            return badPositionIndex(end, size, "end index");
        }
        // end < start
        return format("end index (%s) must not be less than start index (%s)", end, start);
    }

    /**
     * Substitutes each {@code %s} in {@code template} with an argument. These
     * are matched by position: the first {@code %s} gets {@code args[0]}, etc.
     * If there are more arguments than placeholders, the unmatched arguments
     * will be appended to the end of the formatted message in square braces.
     *
     * @param template a non-null string containing 0 or more {@code %s}
     *            placeholders.
     * @param args the arguments to be substituted into the message template.
     *            Arguments are converted to strings using
     *            {@link String#valueOf(Object)}. Arguments can be null.
     */
    // Note that this is somewhat-improperly used from Verify.java as well.
    static String format(String template, @Nullable Object... args) {
        template = String.valueOf(template); // null -> "null"

        // start substituting the arguments into the '%s' placeholders
        StringBuilder builder = new StringBuilder(template.length() + 16 * args.length);
        int templateStart = 0;
        int i = 0;
        while (i < args.length) {
            int placeholderStart = template.indexOf("%s", templateStart);
            if (placeholderStart == -1) {
                break;
            }
            builder.append(template.substring(templateStart, placeholderStart));
            builder.append(args[i++]);
            templateStart = placeholderStart + 2;
        }
        builder.append(template.substring(templateStart));

        // if we run out of placeholders, append the extra args in square braces
        if (i < args.length) {
            builder.append(" [");
            builder.append(args[i++]);
            while (i < args.length) {
                builder.append(", ");
                builder.append(args[i++]);
            }
            builder.append(']');
        }

        return builder.toString();
    }
}
